Wearable pulse pressure wave sensing device

ABSTRACT

Wearable pulse pressure wave sensing devices are presented that generally provide a non-intrusive way to measure a pulse pressure wave travelling through an artery using a wearable device. In one implementation, the device includes an array of pressure sensors disposed on a mounting structure which is attachable to a user on an area proximate to an underlying artery. Each of the pressure sensors is capable of being mechanically coupled to the skin of the user proximate to the underlying artery. In addition, there are one or more arterial location sensors disposed on the mounting structure which identify a location on the user&#39;s skin likely overlying the artery. A pulse pressure wave is then measured using the pressure sensor of the array closest to the identified location.

BACKGROUND

Heart disease is the leading cause of death in the United States,accounting for around six hundred thousand deaths per year (nearly 31%of reported deaths in the United States). High blood pressure(hypertension) is one of the most well-understood risk factors for heartdisease. Hypertension is a risk factor for stroke, heart attack, heartfailure, arterial aneurysm, and is the leading cause of renal failure.In the United States alone, it is estimated that hypertension incursbillions in direct, yearly healthcare costs, and nearly 1,000 deathsdaily. Hypertension is a significant public health issue, and nothingwould save more lives than getting blood pressure under control.

Unfortunately, hypertension has no visible warning signs or symptoms,and many people do not even realize they have it. This is particularlyunfortunate because hypertension is treatable: lifestyle changes,specifically diet and exercise, are known to be effective in preventingthe progression of hypertension. Moreover, numerous medications areavailable to treat hypertension. Therefore, the key to preventing manyheart disease-related deaths may simply be awareness of the risk.

Despite this, blood pressure readings have not gained much attention inthe consumer space. Hypertension is still typically identified throughinfrequent screening (e.g., at an annual exam, health fair, etc.) orwhen seeking healthcare for an unrelated medical issue.

SUMMARY

The wearable pulse pressure wave sensing device implementationsdescribed herein generally provide a non-intrusive way to measuring apulse pressure wave travelling through an artery using a wearabledevice. In one implementation, the device includes a mounting structurewhich is attachable to a user on an area proximate to an underlyingartery. On this mounting structure is disposed an array of pressuresensors, each of which is capable of being mechanically coupled to theskin of the user proximate to the underlying artery. In addition, thereare one or more arterial location sensors disposed on the mountingstructure which identify a location on the user's skin likely overlyingthe artery. The pulse pressure wave is measured using the pressuresensor of the array closest to the identified location.

It should be noted that the foregoing Summary is provided to introduce aselection of concepts, in a simplified form, that are further describedbelow in the Detailed Description. This Summary is not intended toidentify key features or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in determining the scopeof the claimed subject matter. Its sole purpose is to present someconcepts of the claimed subject matter in a simplified form as a preludeto the more detailed description that is presented below.

DESCRIPTION OF THE DRAWINGS

The specific features, aspects, and advantages of the disclosure willbecome better understood with regard to the following description,appended claims, and accompanying drawings where:

FIG. 1 is a simplified diagram of one exemplary implementation of awearable pulse pressure wave sensing device.

FIG. 2 is a flow diagram illustrating an exemplary implementation, insimplified form, of a process for measuring a pulse pressure wavetravelling through an artery using the wearable pulse pressure wavesensing device implementations described herein.

FIG. 3 is a flow diagram illustrating an exemplary implementation, insimplified form, of a process for employing a plurality of arteriallocation sensors, each one of which is located adjacent to a pressuresensor, to identify a location on the user's skin likely overlying anartery being measured and using this information to identify thepressure sensor of the array that is closest to the identified location.

FIG. 4 is a flow diagram illustrating an exemplary implementation, insimplified form, of a process for employing a plurality of image-basedarterial location sensors to identify a location on the user's skinlikely overlying an artery being measured and using this information toidentify the pressure sensor of the array that is closest to theidentified location.

FIG. 5 is a flow diagram illustrating an exemplary implementation, insimplified form, of a process for measuring a pulse pressure wave andusing the morphology of the wave to compute various cardiovascularmetrics.

FIG. 6 is a diagram depicting a general purpose computing deviceconstituting an exemplary system for use with the wearable pulsepressure wave sensing device implementations described herein.

DETAILED DESCRIPTION

In the following description of wearable pulse pressure wave sensingdevice implementations reference is made to the accompanying drawingswhich form a part hereof, and in which are shown, by way ofillustration, specific versions in which the wearable pulse pressurewave sensing device implementations can be practiced. It is understoodthat other implementations can be utilized and structural changes can bemade without departing from the scope thereof.

It is also noted that for the sake of clarity specific terminology willbe resorted to in describing the wearable pulse pressure wave sensingdevice implementations described herein and it is not intended for theseimplementations to be limited to the specific terms so chosen.Furthermore, it is to be understood that each specific term includes allits technical equivalents that operate in a broadly similar manner toachieve a similar purpose. Reference herein to “one implementation”, or“another implementation”, or an “exemplary implementation”, or an“alternate implementation” means that a particular feature, a particularstructure, or particular characteristics described in connection withthe implementation can be included in at least one implementation ofpulse pressure wave sensing. The appearances of the phrases “in oneimplementation”, “in another implementation”, “in an exemplaryimplementation”, and “in an alternate implementation” in various placesin the specification are not necessarily all referring to the sameimplementation, nor are separate or alternative implementations mutuallyexclusive of other implementations. Yet furthermore, the order ofprocess flow representing one or more implementations of wearable pulsepressure wave sensing does not inherently indicate any particular orderor imply any limitations thereof.

As utilized herein, the terms “component,” “system,” “client” and thelike are intended to refer to a computer-related entity, eitherhardware, software (e.g., in execution), firmware, or a combinationthereof. For example, a component can be a process running on aprocessor, an object, an executable, a program, a function, a library, asubroutine, a computer, or a combination of software and hardware. Byway of illustration, both an application running on a server and theserver can be a component. One or more components can reside within aprocess and a component can be localized on one computer and/ordistributed between two or more computers. The term “processor” isgenerally understood to refer to a hardware component, such as aprocessing unit of a computer system.

Furthermore, to the extent that the terms “includes,” “including,”“has,” “contains,” variants thereof, and other similar words are used ineither this detailed description or the claims, these terms are intendedto be inclusive in a manner similar to the term “comprising” as an opentransition word without precluding any additional or other elements.

1.0 Pulse Pressure Wave Sensing

When the human heart expels blood, a pressure wave is created. Thispressure wave travels along the arteries in the body affected by theoverall blood pressure, the lining of the arteries, and thestiffness/compliance of the arteries. A pressure sensor at a given pointin an artery can transduce this pressure as it changes with time andrecord the resulting pulse pressure wave. The pulse pressure wave isformed from the combination of an incident wave generated by thecontraction of the left ventricle of a person's heart and wavesreflected back from the periphery of the arterial system. Pressuresensors generally come in two forms: invasive and non-invasive. Theinvasive form is a catheter inserted in the artery with a pressuresensor on the tip. This type of pressure sensing is the most accurateway to record pulse pressure waves. The non-invasive approach involvesplacing a pressure sensor on the surface of the skin over an artery andapplying force such that the changing intra-arterial pulse pressure istransmitted through the arterial wall to the sensor. Arteries that arecommonly sensed non-invasively are the radial, carotid, and femoralarteries (although any other artery located near the surface of the skincan be sensed as well). A pressure sensor used to transduce pulsepressure waves is often called a tonometer. The morphology of a pulsepressure wave sensed by a tonometer can be analyzed to ascertainimportant information about the state and health of the cardiovascularsystem, as will be described in more detail in the sections to follow.

1.1 Wearable Pulse Pressure Wave Sensing Device

The wearable pulse pressure wave sensing device implementationsdescribed herein are generally applicable to non-invasive tonometricmeasurement of the aforementioned pulse pressure waves. As will beappreciated from the more detailed description that follows, thewearable pulse pressure wave sensing device implementations describedherein are advantageous for various reasons. For example, the wearablepulse pressure wave sensing device implementations described hereinfacilitate a cost effective and easy way to assess cardiovascularhealth. The described implementations can also assist in preventing manyheart-disease-related deaths by making users who have hypertension awareof it. Once a given user is made aware of their having hypertension, thewearable pulse pressure wave sensing device implementations describedherein can facilitate routine monitoring of the user's cardiovascularvital signs, and encourage the user to treat their hypertension byconsulting with a doctor and making appropriate lifestyle changes. Thedescribed implementations also measure a pulse pressure wave at alocation on the body in a non-invasive and non-intrusive (e.g., apassive) manner, and thus allow users to routinely measure/monitor theircardiovascular vital signs without pain and discomfort.

As will also be appreciated from the more detailed description thatfollows, the wearable pulse pressure wave sensing device implementationsdescribed herein can be employed in a variety of applications, and canalso be realized in various types of computing devices. The wearablepulse pressure wave sensing device implementations are also easy tooperate, and are not restricted to being used by a trained medicaltechnician or doctor in a controlled medical setting such as alaboratory or doctor's office.

Further, as the described implementations are wearable on the body of auser, ambulatory automatic tonometry is possible and thus facilitatesthe convenient and automatic measurement of cardiovascular vital signsat one or more opportunistic times during the normal course of a daywhile a user is either stationary or in motion, including while a useris involved in or performing a wide variety of physical activities. Aswill be appreciated from the more detailed description that follows, thewearable pulse pressure wave sensing device implementations describedherein do not require a user to ensure that a pressure sensor directlyoverlies an artery. Rather, the implementations described hereinautomatically choose a pressure sensor and senses a tonometry signalwithout any precise manipulation of the device.

FIG. 1 illustrates one exemplary implementation of the wearable pulsepressure wave sensing device. The device 100 includes a mountingstructure 102 which is attachable to a user on an area proximate to anunderlying artery. In addition, the device 100 includes an array ofpressure sensors disposed on the mounting structure 102. Each pressuresensor 104 of the array is capable of being mechanically coupled to theskin of the user proximate to the underlying artery. The wearable pulsepressure wave sensing device 100 further includes one or more arteriallocation sensors 106 (a plurality of which are shown in FIG. 1) disposedon the mounting structure 102 that identify a location on the user'sskin likely overlying the artery. A pulse pressure wave travellingthrough the artery is then measured using the pressure sensor 104 of thearray identified as being closest to the identified location.

In one version, the pressure sensors are of the mechanical type, suchas, but without limitation, piezoresistive pressure sensors that sensethe motion of an underlying artery through the skin when the pulsearrives. The shape of the surface of each pressure sensor that faces theuser can be any desired (square, rectangular, triangular, and so on).The pressure sensors can all have the same facing surface, all differentfacing surfaces, or any combination of facing surfaces.

In one version, the pressure sensors are coated with a skin-sensorinterface material that contacts the skin of the user and propagatespressure waves representing the movement of the skin owing to a pulsepressure wave travelling through an artery underlying the sensors. Inone version, each pressure sensor is coated individually such that itscoating does not extend over any other of the pressure sensors. Inanother version, two or more of the pressure sensors have a commoncoating. In one version, the coating is a single layer of cured siliconegel. The profile shape of the coating can be anything practical thatensures adequate contact with the user's skin but does not cause unduediscomfort to the user. For example, in one version the coating takesthe shape of a spherical cap (or similar curved shape) protruding fromthe mounting structure. The stiffness of the coating can range betweenhard and soft. In operation, the coated pressure sensors are presseddown onto the skin of the user to ensure efficient transmission of themotion of the underlying artery to the sensors. A hard coating ensuresbetter transmission of the movements caused by a pulse pressure wavepassing through the artery, but even though only a slight pressure isapplied to the skin, it would not be as comfortable to the user as asofter coating. Although a soft coating would be more comfortable than ahard coating, it would not transmit the motion as well. Thus, in oneversion, the coating stiffness is made so as to balance efficient motiontransmission with comfort. Alternately, in one version the coatedpressure sensors have a multi-layer construction that attempts tomaximize the transmission of the movements caused by a pulse pressurewave passing through the artery, while at the same time attempting tomaximize the user's comfort. In this version, there is a skininterfacing layer made of a non-sensitizing, hypo-allergenic andnon-irritating material (e.g., a soft, cured silicone gel). Between theskin interfacing layer and the pressure sensor is a layer made of amaterial that optimally transmits the arterial pressure wave movement(e.g., a hard, cured silicone gel).

In one version, the coated pressure sensors protrude from theaforementioned mounting structure with a fixed length. This fixed lengthcan be any desired for each of the coated pressure sensors. In oneversion, all of the coated pressure sensors have the same length, and inother versions one or more of the coated pressure sensors have adifferent length in comparison with the other sensors.

Alternately, the coated pressure sensors can be extendable andretractable so as to protrude from the mounting structure withadjustable lengths. In one version, an extendable coated pressure sensoris configured in any appropriate manner to be spring loaded (such as viaa pogo pin arrangement). A spring-loaded coated pressure sensor extendsout to meet the surface of the skin, and to impart a slight pressurethereon. This same extendable coated pressure measurement sensor schemecan be realized using other methods, such as with electro-mechanicalactuators, or micro-fluidic pumps that expand and contract an air orfluid-filled bladder (which in turn extends and retract a coatedpressure sensor). In the latter two versions, the distance that thecoated pressure sensors are extended and the amount of pressure theyexert on the skin can be controlled and set to a level that ensuresefficient transmission of arterial motion, while not causing discomfortto the user.

The array of pressure sensors can form any desired pattern. For example,in one version, the sensors form a line that can be oriented in anydirection relative the user's body. In another version, three pressuresensors are employed to form a triangular pattern. This version canprovide a larger effective “field of view” of the underlying artery thanthe linear version. For the purposes of this description, the phrase“field of view” refers to the area covered by the sensors. In yetanother version, a grid of four or more pressure sensors is employed(such as shown in FIG. 1). The grid can exhibit rectangular, triangular,or random spacing of the sensors. The sensors can also be smaller inorder to fit more in the available space.

In one version, the aforementioned mounting structure onto which thecoated pressure sensors are disposed is capable of being held in placeon the user in such a way that the coated sensors are in contact withthe skin of the user in the vicinity of an underlying artery and apply adownward pressure. For example, in one version, the coated pressuresensors are mounted on a side of a band that is adhered to, or wrappedaround and tightened against (via any appropriate fastening scheme thatthe tightness is dynamically adjustable), a portion of a user's bodyoverlying an artery. In the case where the band is wrapped around aportion of the user's body, it can be configured to wrap around aperson's wrist (like a watch), or forearm, or upper arm (like an armbandcommonly used to hold mobile phones or music players during exercise),or torso, or upper leg, or lower leg, or ankle, among other places. Ingeneral, any place on a person's body that a strap can be wrapped aroundand tightened, and which movement in an underlying artery can be sensed,would be a viable location. In the case where the band is adhered to thebody, not only are the foregoing locations feasible but others as well.

In one version, the location on the band where the pressure sensors aremounted on the mounting structure is flexible so as to readily conformto the contours of the portion of the user's body the band covers. Inanother version, the location on the band where the pressure sensors aremounted on the mounting structure is rigid. For example, the band caninclude a rigid platform for mounting the pressure sensors which hasflexible portions extending in both directions for attaching it to thebody of the user. In the case where the band is attached around theuser's wrist, it can resemble a watch with the watch body forming theaforementioned rigid portion. The former flexible version isadvantageous in that the coated pressure sensors are better able tocontact the surface of the user's skin and remain in contact when slightpressure is applied thereto (such as by tightening the strap which iswrapped around a portion of the user's body). This ensures an efficienttransfer of arterial motion to the pressure sensors and can be morecomfortable to the user than a rigid version. However, the realizationof the aforementioned rigid version is less complicated owing to theaforementioned rigid mounting platform, albeit with possibly varyingcontact and contact pressure between the coated pressure sensors.

1.1.1 Identifying the Pressure Sensor Closest to the Identified Location

One or more arterial location sensors are employed to identify alocation on the user's skin likely overlying the artery being measured.This information is then used to identify the pressure sensor of thearray that is closest to the identified location. As indicatedpreviously, the user is not required to precisely place the wearablepulse pressure wave sensing device so that one of its pressure sensorsdirectly overlies an artery. Thus, it is advantageous to automaticallyidentify which of the pressure sensors is closest to the likely locationof an underlying artery because a pressure sensor located nearest anartery will typically sense the motion caused by a pulse pressure wavepassing through the artery at that location better than a pressuresensor that is placed on the skin at a location offset from theunderlying artery.

In one version, the arterial location sensor(s) are employed to identifywhere on the portion of the user's body covered by the wearable pulsepressure wave sensing device that maximum skin displacement occurs as apulse pressure wave passes through the underlying artery. The locationof maximum skin displacement is deemed to be a probable location of anunderlying artery. In one version, the arterial location sensors takethe form of reflected optical sensors (e.g., the type employing a lightemitting diode (LED) and photodiode). In another version, the arteriallocation sensors take the form of ultrasonic sensors.

In operation, a computer-implemented process can be used to measure apulse pressure wave travelling through an artery. Referring to FIG. 2,in one version, a computing device (such as an appropriate one describedin the forthcoming exemplary operating environments section) employs theone or more arterial location sensors to identify a location on theuser's skin in the area proximate to the artery being measured thatexhibits the greatest displacement of the user's skin when a pulsepressure wave passes through the artery in that area (process action200). For example, in the case where the arterial location sensors arereflected optical sensors or ultrasonic sensors, conventionaldisplacement measuring methods can be employed to accomplish theforegoing task. It is then determined which pressure sensor of the arrayof pressure sensors is closest to the identified location on the user'sskin (process action 202). That pressure sensor is selected (processaction 204), and a pulse pressure wave travelling through the artery ismeasured using the selected pressure sensor (process action 206).

In one version, a plurality of arterial location sensors are used toidentify the aforementioned probable location of the underlying artery.In this version, each pressure sensor has an adjacently-located arteriallocation sensor (such as shown in FIG. 1). If a particular arteriallocation sensor measures a skin displacement that is greater than theother arterial location sensors, then its adjacently-located pressuresensor is designated the closest pressure sensor to the underlyingartery. More particularly, referring to FIG. 3, in one implementationthe following process is employed to find the closest pressure sensor.First, multiple arterial location sensors are employed to measure thedisplacement of the user's skin when a pulse pressure wave passesthrough the underlying artery (process action 300). Each arteriallocation sensor is associated with and located adjacent to a differentpressure sensor of the array of pressure sensors. It is then determinedwhich of the multiple arterial location sensors measures the greatestdisplacement of the user's skin (process action 302). The location onthe user's skin where the identified arterial location sensor measuredthe greatest displacement is then designated as the probable location ofthe underlying artery (process action 304). The pressure sensorassociated with the arterial location sensor that measured the greatestdisplacement of the user's skin is then identified (process action 306),and is designated as the closest pressure sensor to the underlyingartery (process action 308).

In one version, one or more image-based arterial location sensors (e.g.,visible or infrared light charge-coupled devices) are used to identifythe aforementioned probable location of the underlying artery. In thisversion, the image-based sensors are mounted around or near the pressuresensor array, and calibrated using conventional methods so that pixelsin the images captured are mapped to physical locations relative to eachpressure sensor of the array. Given this configuration, referring toFIG. 4, in one implementation the following process is employed toselect a pressure sensor and use it to measure a pulse pressure wavetravelling through an artery. Images are captured using the one or moreimage-based arterial location sensors (process action 400). Conventionalimage analysis is then applied to the captured images to visuallyidentify the location on the user's skin likely overlying the arterybeing measured (process action 402). It is next determined whichpressure sensor of the array of pressure sensors is closest to theidentified location on the user's skin using the aforementioned mappedlocations of the pressure sensors (process action 404). That pressuresensor is selected (process action 406), and a pulse pressure wavetravelling through the artery is measured using the selected pressuresensor (process action 408).

It is noted that in any of the foregoing arterial location sensorversions, once one of the pressure sensors is selected, the otherpressure sensors can optionally be turned off. Further, if the otherpressure sensors are turned off, they can be periodically reactivatedand the appropriate foregoing process repeated to select the pressuresensor that will be used to measure future pulse pressure wavestravelling through an artery.

1.1.2 Removing Non-Arterial Motion Contribution

It is noted that the pressure sensors not only measure arterialmovements, but also noise owing to other movements of the user. As thewearable pulse pressure wave sensing device is meant to be worn by theuser for extended periods of time, the user may be in motion when apulse pressure wave is measured. In the case of piezoresistive pressuresensors, this ambulatory motion will be sensed and is indistinguishablefrom arterial motion. To compensate for this noise motion, the signaloutput by a pressure sensor is filtered to remove as much non-arterialmotion contribution as possible.

In one version, the non-arterial motion contribution in the signal isfiltered out using the pressure sensor signals themselves. In simplifiedterms, this entails using conventional methods to identify the part ofthe output signal in each pressure sensor that is substantiallyconsistent across the sensors. This consistent contribution approximatesthe non-arterial motion contribution since it should be similar for eachsensor, whereas the arterial motion contribution will vary amongst thepressure sensors depending on their relative locations from theunderlying artery. The non-arterial motion contribution to the signal ofthe pressure sensor previously identified as being closest to the likelylocation of the underlying artery is then subtracted out usingconventional signal processing methods, leaving an approximation of thearterial motion contribution. This arterial motion contribution portionof the output signal will exhibit a well-known pulse waveform whosemorphology can be analyzed to derive a plurality of cardiovascularmetrics as will be described in more detail later in this description.

In alternate versions, the non-arterial motion contribution in thepressure sensor signals is filtered out using one or more non-arterialmotion sensors. More particularly, referring once again to FIG. 1, inone version, the aforementioned wearable pulse pressure wave sensingdevice 100 also includes one or more non-arterial motion sensors 108(two of which are shown in FIG. 1) disposed on the mounting structure102. The non-arterial motion sensor(s) 108 measure the motion of theuser's body in the area proximate to the underlying artery that is notcaused by motion of the artery. The non-arterial movement signal derivedfrom the non-arterial motion sensor(s) 108 is then removed from thesignal of the pressure sensor previously identified as being closest tothe likely location of the underlying artery using conventional signalprocessing methods. This leaves an approximation of the arterial motioncontribution. As indicated previously, this arterial motion contributionportion of the output signal will exhibit a well-known pulse waveformwhose morphology can be analyzed to derive a plurality of cardiovascularmetrics.

In one implementation, an accelerometer or gyroscope, or both, areemployed as the non-arterial motion sensors. The accelerometer directlymeasures the non-arterial movement that introduces noise into thepressure sensor output signals. A gyroscope measures angular movement,but the output can be readily analyzed using conventional methods toderive linear values similar to those measured by an accelerometer. Incases where both an accelerometer and gyroscope are employed theaccelerometer output and the converted gyroscope output can be combinedin any appropriate conventional manner to produce a consensus signalrepresenting non-arterial movement.

1.1.3 Cardiovascular Metrics

As indicated previously, the pulse waveforms extracted from the outputsignal of the pressure sensor selected as closest to the likely locationof an underlying artery can be analyzed using conventional methods tomeasure various cardiovascular metrics. For example, but withoutlimitation, the pulse waveforms can be used to determine the heart rateof a person wearing the pulse pressure wave sensing device, as well asvariations in the person's hear rate over time. In addition, anextracted pulse waveform can be used to compute a person's augmentationindex. The augmentation index measures how hard the heart is workingagainst the pressure waves reflected back by the periphery of thecirculatory system.

The time of arrival of a pulse pressure wave is also useful informationand can be determined from the pulse waveform. This arrival time can beused in conjunction with other data to calculate pulse transit time(PTT) and pulse wave velocity (PWV). Generally speaking, PTT refers tothe amount of time it takes for a pulse pressure wave that is generatedby blood being expelled from a user's heart to travel through the user'sarteries from one arterial site on the user's body to another arterialsite on the user's body. For example, in the wearable pulse pressurewave sensing device implementations described herein where the deviceattaches to a user's wrist, the PTT refers to the amount of time ittakes for a pulse pressure wave to travel from the user's heart, throughtheir arteries, to an artery on the wrist (e.g., radial artery). As isappreciated in the arts of medicine and cardiovascular health, there isa known correlation between pulse-transit time and other cardiovascularmetrics such as blood pressure, arterial compliance, and the hardeningof artery walls. Although other body metrics (such as the user's height,weight and age, and the arterial distance between the just-described twoarterial sites on the user's body, among other types of body metrics)influence the user's blood pressure, the PTT measurement can be used todetermine the user's blood pressure based on the just-described knowncorrelation between PTT and blood pressure.

As for PWV, this term is used to refer to the speed at which a pulsepressure wave travels through a user's arteries from one arterial siteon the user's body to another arterial site on the user's body. In thepreviously-described exemplary version where the pulse pressure wavesensing device is worn on a user's wrist, PWV refers to the averagespeed at which the pulse pressure wave travels from the user's heart,through their arteries, to the wrist. As is appreciated in the arts ofmedicine and cardiovascular health, there is a known correlation betweenpulse-wave velocity and cardiovascular diseases such as hypertension.More particularly, as a person ages their arteries generally getstiffer. This increasing arterial stiffness makes the person's heartwork harder and also makes the pulse pressure wave travel faster throughtheir arteries, thus increasing their risk of cardiovascular diseasessuch as hypertension.

Computation of the foregoing cardiovascular metrics, along with thepreviously-described processing of the signals output from the pressuresensors, arterial location sensor(s) and non-arterial motion sensor(s)is accomplished in one implementation using one or more computingdevices (such as one of those described in the forthcoming exemplaryoperating environments section), and a computer program executingthereon. Referring again to FIG. 1, in one implementation, the wearablepulse pressure wave sensing device 100 also includes a computing device110 disposed on the mounting structure 102 that is employed for theforegoing processing and computations. In addition, the wearable pulsepressure wave sensing device 100 can optionally include an appropriateconventional storage component 112 for storing any data needed toaccomplish the aforementioned processing and computations, as wellstoring the results of the processing and computations. Still further,the wearable pulse pressure wave sensing device 100 can optionallyinclude an appropriate conventional communications component 114 forcommunicating with the remote computing devices. For example, thecommunications component can be employed to receive data needed toperform the aforementioned processing and computations, or to transmitcomputed cardiovascular metrics. Any communication scheme can beemployed. For example, communication can be via a computer network suchas the Internet or a proprietary intranet. It is noted that thedashed-line boxes used in FIG. 1 indicate optional components.

In view of the foregoing and referring to FIG. 5, in one version, thecomputing device is directed by the program modules of the computerprogram to first receive signals output from the one or more arteriallocation sensors (process action 500). A location on the user's skin inthe area proximate to the artery which exhibits the greatestdisplacement when a pulse pressure wave passes through the artery isthen identified using the received signals output from the one or morearterial location sensors (process action 502). It is next determinedwhich pressure sensor of the array of pressure sensors is closest to theidentified location on the user's skin (process action 504), and thatpressure sensor is selected (process action 506). A signal output fromthe selected pressure sensor when a pulse pressure wave is travellingthrough the artery is received (process action 508), and it is analyzedto determine various cardiovascular metrics (process action 510). Thesemetrics can be stored or transmitted, or both.

1.1.4 Wrist-Band Implementations

As indicated previously, the wearable pulse pressure wave sensing deviceimplementations described herein include versions that are worn on thewrist. These wrist-band versions provide an opportunity to includeadditional advantageous features and configurations. For example, in oneversion, the wrist-band takes the form of a wrist watch, and in anotherthe wrist-band takes the form of a so-called “smart watch” with all itsattendant computing, display and communication capabilities. It is notedthat given the user interface capabilities of a smart watch, thewearable sensing implementations described herein employing this formcan be configured via conventional means to display information to thewearer. For example, instructions for operating the wrist-bandimplementations can be displayed to the user, as well as the computedcardiovascular metrics.

It is further noted that given the proximity of the underside (i.e.,palm side) of the wrist to arteries (such as the radial artery),placement of the pressure sensors, arterial location sensor(s) andnon-arterial motion sensor(s) on the part of a watchband that touchesthis portion of the wrist is advantageous.

2.0 Exemplary Operating Environments

The wearable pulse pressure wave sensing device implementationsdescribed herein are operational using numerous types of general purposeor special purpose computing system environments or configurations. FIG.6 illustrates a simplified example of a general-purpose computer systemwith which various aspects and elements of wearable pulse pressure wavesensing device, as described herein, may be implemented. It is notedthat any boxes that are represented by broken or dashed lines in thesimplified computing device 10 shown in FIG. 6 represent alternateimplementations of the simplified computing device. As described below,any or all of these alternate implementations may be used in combinationwith other alternate implementations that are described throughout thisdocument. The simplified computing device 10 is typically found indevices having at least some minimum computational capability such aspersonal computers (PCs), server computers, handheld computing devices,laptop or mobile computers, communications devices such as cell phonesand personal digital assistants (PDAs), multiprocessor systems,microprocessor-based systems, set top boxes, programmable consumerelectronics, network PCs, minicomputers, mainframe computers, and audioor video media players.

To realize the wearable pulse pressure wave sensing deviceimplementations described herein, the device should have a sufficientcomputational capability and system memory to enable basic computationaloperations. In particular, the computational capability of thesimplified computing device 10 shown in FIG. 6 is generally illustratedby one or more processing unit(s) 12, and may also include one or moregraphics processing units (GPUs) 14, either or both in communicationwith system memory 16. Note that that the processing unit(s) 12 of thesimplified computing device 10 may be specialized microprocessors (suchas a digital signal processor (DSP), a very long instruction word (VLIW)processor, a field-programmable gate array (FPGA), or othermicro-controller) or can be conventional central processing units (CPUs)having one or more processing cores.

In addition, the simplified computing device 10 may also include othercomponents, such as, for example, a communications interface 18. Thesimplified computing device 10 may also include one or more conventionalcomputer input devices 20 (e.g., touchscreens, touch-sensitive surfaces,pointing devices, keyboards, audio input devices, voice or speech-basedinput and control devices, video input devices, haptic input devices,devices for receiving wired or wireless data transmissions, and thelike) or any combination of such devices.

Similarly, various interactions with the simplified computing device 10and with any other component or feature of wearable sensing, includinginput, output, control, feedback, and response to one or more users orother devices or systems associated with wearable sensing, are enabledby a variety of Natural User Interface (NUI) scenarios. The NUItechniques and scenarios enabled by wearable sensing include, but arenot limited to, interface technologies that allow one or more users userto interact with wearable sensing in a “natural” manner, free fromartificial constraints imposed by input devices such as mice, keyboards,remote controls, and the like.

Such NUI implementations are enabled by the use of various techniquesincluding, but not limited to, using NUI information derived from userspeech or vocalizations captured via microphones or other sensors. SuchNUI implementations are also enabled by the use of various techniquesincluding, but not limited to, information derived from a user's facialexpressions and from the positions, motions, or orientations of a user'shands, fingers, wrists, arms, legs, body, head, eyes, and the like,where such information may be captured using various types of 2D ordepth imaging devices such as stereoscopic or time-of-flight camerasystems, infrared camera systems, RGB (red, green and blue) camerasystems, and the like, or any combination of such devices. Furtherexamples of such NUI implementations include, but are not limited to,NUI information derived from touch and stylus recognition, gesturerecognition (both onscreen and adjacent to the screen or displaysurface), air or contact-based gestures, user touch (on varioussurfaces, objects or other users), hover-based inputs or actions, andthe like. Such NUI implementations may also include, but are notlimited, the use of various predictive machine intelligence processesthat evaluate current or past user behaviors, inputs, actions, etc.,either alone or in combination with other NUI information, to predictinformation such as user intentions, desires, and/or goals. Regardlessof the type or source of the NUI-based information, such information maythen be used to initiate, terminate, or otherwise control or interactwith one or more inputs, outputs, actions, or functional features ofwearable pulse pressure wave sensing device implementations describedherein.

However, it should be understood that the aforementioned exemplary NUIscenarios may be further augmented by combining the use of artificialconstraints or additional signals with any combination of NUI inputs.Such artificial constraints or additional signals may be imposed orgenerated by input devices such as mice, keyboards, and remote controls,or by a variety of remote or user worn devices such as accelerometers,electromyography (EMG) sensors for receiving myoelectric signalsrepresentative of electrical signals generated by user's muscles,heart-rate monitors, galvanic skin conduction sensors for measuring userperspiration, wearable or remote biosensors for measuring or otherwisesensing user brain activity or electric fields, wearable or remotebiosensors for measuring user body temperature changes or differentials,and the like. Any such information derived from these types ofartificial constraints or additional signals may be combined with anyone or more NUI inputs to initiate, terminate, or otherwise control orinteract with one or more inputs, outputs, actions, or functionalfeatures of wearable pulse pressure wave sensing device implementationsdescribed herein.

The simplified computing device 10 may also include other optionalcomponents such as one or more conventional computer output devices 22(e.g., display device(s) 24, audio output devices, video output devices,devices for transmitting wired or wireless data transmissions, and thelike). Note that typical communications interfaces 18, input devices 20,output devices 22, and storage devices 26 for general-purpose computersare well known to those skilled in the art, and will not be described indetail herein.

The simplified computing device 10 shown in FIG. 6 may also include avariety of computer-readable media. Computer-readable media can be anyavailable media that can be accessed by the computer 10 via storagedevices 26, and can include both volatile and nonvolatile media that iseither removable 28 and/or non-removable 30, for storage of informationsuch as computer-readable or computer-executable instructions, datastructures, program modules, or other data. Computer-readable mediaincludes computer storage media and communication media. Computerstorage media refers to tangible computer-readable or machine-readablemedia or storage devices such as digital versatile disks (DVDs), blu-raydiscs (BD), compact discs (CDs), floppy disks, tape drives, hard drives,optical drives, solid state memory devices, random access memory (RAM),read-only memory (ROM), electrically erasable programmable read-onlymemory (EEPROM), CD-ROM or other optical disk storage, smart cards,flash memory (e.g., card, stick, and key drive), magnetic cassettes,magnetic tapes, magnetic disk storage, magnetic strips, or othermagnetic storage devices. Further, a propagated signal is not includedwithin the scope of computer-readable storage media.

Retention of information such as computer-readable orcomputer-executable instructions, data structures, program modules, andthe like, can also be accomplished by using any of a variety of theaforementioned communication media (as opposed to computer storagemedia) to encode one or more modulated data signals or carrier waves, orother transport mechanisms or communications protocols, and can includeany wired or wireless information delivery mechanism. Note that theterms “modulated data signal” or “carrier wave” generally refer to asignal that has one or more of its characteristics set or changed insuch a manner as to encode information in the signal. For example,communication media can include wired media such as a wired network ordirect-wired connection carrying one or more modulated data signals, andwireless media such as acoustic, radio frequency (RF), infrared, laser,and other wireless media for transmitting and/or receiving one or moremodulated data signals or carrier waves.

Furthermore, software, programs, and/or computer program productsembodying some or all of the various wearable pulse pressure wavesensing implementations described herein, or portions thereof, may bestored, received, transmitted, or read from any desired combination ofcomputer-readable or machine-readable media or storage devices andcommunication media in the form of computer-executable instructions orother data structures. Additionally, the claimed subject matter may beimplemented as a method, apparatus, or article of manufacture usingstandard programming and/or engineering techniques to produce software,firmware, hardware, or any combination thereof to control a computer toimplement the disclosed subject matter. The term “article ofmanufacture” as used herein is intended to encompass a computer programaccessible from any computer-readable device, or media.

The wearable pulse pressure wave sensing implementations describedherein may be further described in the general context ofcomputer-executable instructions, such as program modules, beingexecuted by a computing device. Generally, program modules includeroutines, programs, objects, components, data structures, and the like,that perform particular tasks or implement particular abstract datatypes. The wearable pulse pressure wave sensing implementations may alsobe practiced in distributed computing environments where tasks areperformed by one or more remote processing devices, or within a cloud ofone or more devices, that are linked through one or more communicationsnetworks. In a distributed computing environment, program modules may belocated in both local and remote computer storage media including mediastorage devices. Additionally, the aforementioned instructions may beimplemented, in part or in whole, as hardware logic circuits, which mayor may not include a processor.

Alternatively, or in addition, the functionality described herein can beperformed, at least in part, by one or more hardware logic components.For example, and without limitation, illustrative types of hardwarelogic components that can be used include field-programmable gate arrays(FPGAs), application-specific integrated circuits (ASICs),application-specific standard products (ASSPs), system-on-a-chip systems(SOCs), complex programmable logic devices (CPLDs), and so on.

3.0 Other Implementations

It is noted that any or all of the aforementioned implementationsthroughout the description may be used in any combination desired toform additional hybrid implementations. In addition, although thesubject matter has been described in language specific to structuralfeatures and/or methodological acts, it is to be understood that thesubject matter defined in the appended claims is not necessarily limitedto the specific features or acts described above. Rather, the specificfeatures and acts described above are disclosed as example forms ofimplementing the claims.

What has been described above includes example implementations. It is,of course, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing the claimedsubject matter, but one of ordinary skill in the art may recognize thatmany further combinations and permutations are possible. Accordingly,the claimed subject matter is intended to embrace all such alterations,modifications, and variations that fall within the spirit and scope ofthe appended claims.

In regard to the various functions performed by the above describedcomponents, devices, circuits, systems and the like, the terms(including a reference to a “means”) used to describe such componentsare intended to correspond, unless otherwise indicated, to any componentwhich performs the specified function of the described component (e.g.,a functional equivalent), even though not structurally equivalent to thedisclosed structure, which performs the function in the hereinillustrated exemplary aspects of the claimed subject matter. In thisregard, it will also be recognized that the foregoing implementationsinclude a system as well as a computer-readable storage media havingcomputer-executable instructions for performing the acts and/or eventsof the various methods of the claimed subject matter.

There are multiple ways of realizing the foregoing implementations (suchas an appropriate application programming interface (API), tool kit,driver code, operating system, control, standalone or downloadablesoftware object, or the like), which enable applications and services touse the implementations described herein. The claimed subject mattercontemplates this use from the standpoint of an API (or other softwareobject), as well as from the standpoint of a software or hardware objectthat operates according to the implementations set forth herein. Thus,various implementations described herein may have aspects that arewholly in hardware, or partly in hardware and partly in software, orwholly in software.

The aforementioned systems have been described with respect tointeraction between several components. It will be appreciated that suchsystems and components can include those components or specifiedsub-components, some of the specified components or sub-components,and/or additional components, and according to various permutations andcombinations of the foregoing. Sub-components can also be implemented ascomponents communicatively coupled to other components rather thanincluded within parent components (e.g., hierarchical components).

Additionally, it is noted that one or more components may be combinedinto a single component providing aggregate functionality or dividedinto several separate sub-components, and any one or more middle layers,such as a management layer, may be provided to communicatively couple tosuch sub-components in order to provide integrated functionality. Anycomponents described herein may also interact with one or more othercomponents not specifically described herein but generally known bythose of skill in the art.

4.0 Claim Support and Further Implementations

The following paragraphs summarize various examples of implementationswhich may be claimed in the present document. However, it should beunderstood that the implementations summarized below are not intended tolimit the subject matter which may be claimed in view of the foregoingdescriptions. Further, any or all of the implementations summarizedbelow may be claimed in any desired combination with some or all of theimplementations described throughout the foregoing description and anyimplementations illustrated in one or more of the figures, and any otherimplementations described below. In addition, it should be noted thatthe following implementations are intended to be understood in view ofthe foregoing description and figures described throughout thisdocument.

In one implementation, a wearable pulse pressure wave sensing deviceincludes a mounting structure which is attachable to a user on an areaproximate to an underlying artery; an array of pressure sensors disposedon the mounting structure, each of which is capable of beingmechanically coupled to the skin of the user proximate to the underlyingartery; and one or more arterial location sensors disposed on themounting structure which identify a location on the user's skin likelyoverlying the artery. The pulse pressure wave is measured using thepressure sensor of the array closest to the identified location.

In one implementation, the pressure sensors in the array of pressuresensors are coated with a skin-sensor interface material having a shapewhich protrudes from the mounting structure so as to contact the skin ofthe user whenever the wearable pulse pressure wave sensing device isworn by the user. In one version, the pressure sensors of the array ofpressure sensors are individually coated with the skin-sensor interfacematerial. In another version, two or more pressure sensors in the arrayof pressure sensors are collectively coated with the skin-sensorinterface material. In one version, one or more of the coated pressuresensors include a single skin interfacing and arterial pressure wavemovement transmission layer that is made of a material that iscomfortable on the skin of the user and efficiently transmits arterialpressure wave movement. In another version, one or more of the coatedpressure sensors include a multi-layer construction including a skininterfacing layer made of a material that is comfortable on the skin ofthe user, and a layer disposed between the skin interfacing layer andthe pressure sensor that is made of a material that efficientlytransmits arterial pressure wave movement. As indicated previously, theimplementations and versions described in any of the previous paragraphsin this section may also be combined with each other, and with one ormore of the implementations and versions described prior to thissection. For example, some or all of the preceding implementations andversions may be combined with the foregoing implementation where one ormore of the coated pressure sensors include a single skin interfacingand arterial pressure wave movement transmission layer, or where one ormore of the coated pressure sensors include a multi-layer construction.

In one implementation, one or more of the pressure sensors include anapparatus that extends and retracts to vary the distance the coatedpressure sensor protrudes from the mounting structure. In one version,the apparatus includes at least one of a spring-loaded pogo pin, or anelectro-mechanical actuator, or a micro-fluidic pump with a fluid-filledor air-filled bladder. As indicated previously, the implementations andversions described in any of the previous paragraphs in this section mayalso be combined with each other, and with one or more of theimplementations and versions described prior to this section. Forexample, some or all of the preceding implementations and versions maybe combined with the foregoing implementation where one or more of thepressure sensors include an apparatus that extends and retracts to varythe distance the coated pressure sensor protrudes from the mountingstructure.

In one implementation, the aforementioned one or more arterial locationsensors identify a location on the user's skin in the area proximate tothe underlying artery which exhibits the greatest displacement of theuser's skin as the location likely overlying the artery. In one version,the arterial location sensors include reflected optical sensors orultrasonic sensors.

In one implementation, wearable pulse pressure wave sensing devicefurther includes one or more non-arterial motion sensors disposed on themounting structure which measure the motion of the user's body in thearea proximate to the underlying artery that is not caused by motion ofthe artery. A signal or signals output from the one or more non-arterialmotion sensors representing the non-arterial motion of the user's bodyin the area proximate to the underlying artery are employed to remove aportion of a signal output from the pressure sensor of the arrayidentified as being most closely overlying the likely location of theartery attributable to non-arterial motion. In one version, the one ormore non-arterial motion sensors include an accelerometer or gyroscope,or both.

In one implementation, the aforementioned mounting structure includes aband which is either adhered to the area proximate to the underlyingartery, or wrapped around and tightened against the area. In oneversion, the area proximate to the underlying artery is the user'swrist.

In one implementation, a wearable pulse pressure wave sensing device isused in a process for measuring a pulse pressure wave travelling throughan artery. The wearable pulse pressure wave sensing device includes anarray of pressure sensors which are mechanically coupled to the skin ofa user proximate to the artery. The process uses a computing device toperform the following process actions. One or more arterial locationsensors of the wearable pulse pressure wave sensing device are employedto identify a location on the user's skin in the area proximate to theartery which exhibits the greatest displacement of the user's skin whena pulse pressure wave passes through the artery in the area. It is thendetermined which pressure sensor of the array of pressure sensors isclosest to the identified location on the user's skin, and the pressuresensor determined to be closest to the identified location is selected.A pulse pressure wave travelling through the artery is then measuredusing the selected pressure sensor.

In one implementation, the process action of employing one or morearterial location sensors to identify a location on the user's skin inthe area proximate to the artery which exhibits the greatestdisplacement of the user's skin when a pulse pressure wave passesthrough the artery in the area, includes the actions of employingmultiple arterial location sensors to measure the displacement of theuser's skin when a pulse pressure wave passes through the underlyingartery, each arterial location sensor being associated with and locatedadjacent to a different pressure sensor of the array of pressuresensors; identifying which of the multiple arterial location sensorsmeasures the greatest displacement of the user's skin when a pulsepressure wave passes through the artery; and designating a location onthe user's skin where the identified arterial location sensor measuredthe greatest displacement of the user's skin as a probable location ofthe underlying artery. In one version, the process action of determiningwhich pressure sensor of the array of pressure sensors is closest to theidentified location on the user's skin, includes the actions ofidentifying the pressure sensor associated with the arterial locationsensor that measured the greatest displacement of the user's skin when apulse pressure wave passes through the artery; and designating theidentified pressure sensor as the closest pressure sensor to theunderlying artery.

In one implementation, the process actions of employing one or morearterial location sensors to identify a location on the user's skin inthe area proximate to the artery which exhibits the greatestdisplacement of the user's skin when a pulse pressure wave passesthrough the artery in the area, and determining which pressure sensor ofthe array of pressure sensors is closest to the identified location onthe user's skin, include the following actions. One or more arteriallocation sensors are employed to measure the displacement of the user'sskin when a pulse pressure wave passes through the underlying artery.Each arterial location sensor includes an image-based arterial locationsensor that has been calibrated so that pixels in the images captured bythe image-based arterial location sensor are mapped to locationsrelative to each pressure sensor of the array. Images of the user's skinare captured using the one or more arterial location sensors; thecaptured images are analyzed to visually identify the location of thegreatest displacement of the user's skin when a pulse pressure wavepasses through the artery; and it is determined which pressure sensor ofthe array of pressure sensors is closest to the identified location onthe user's skin using the mapped locations of the pressure sensors.

In one implementation, a wearable pulse pressure wave sensing device ispart of a system for analyzing a pulse pressure wave travelling throughan artery of a user. This system includes a band which is either adheredto an area proximate to an underlying artery of the user's body, orwrapped around and tightened against the area; an array of pressuresensors disposed on the band, each of which is mechanically coupled tothe skin of the user proximate to the underlying artery; and one or morearterial location sensors disposed on the band which identify a locationon the user's skin likely overlying the artery. In addition the systemincludes a computing device which executes program modules of a computerprogram. The computing device is directed by the program modules of thecomputer program to receive signals output from the one or more arteriallocation sensors; identify a location on the user's skin in the areaproximate to the artery which exhibits the greatest displacement of theuser's skin when a pulse pressure wave passes therethrough using thereceived signals output from the one or more arterial location sensors;determine which pressure sensor of the array of pressure sensors isclosest to the identified location on the user's skin; select thepressure sensor determined to be closest to the identified location;receive a signal output from the selected pressure sensor when a pulsepressure wave is travelling through the artery; and analyze the receivedpressure sensor signal. In one version, the program module for analyzingthe received pressure sensor signal, includes sub-modules fordetermining at least one of a heart rate of the user person wearing thepulse pressure wave sensing device, variations in the user's heart rateover time, the user's augmentation index which is computed using a pulsewaveform extracted from the received pressure sensor signal, and a timeof arrival of the pulse pressure wave which is used in conjunction withother data to calculate pulse transit time or pulse wave velocity orboth.

In various implementations, a pulse wave measuring process isimplemented by a step for measuring a pulse pressure wave travellingthrough an artery using a pressure sensor of an array of pressuresensors which are mechanically coupled to the skin of a user proximateto the artery.

For example, in one implementation, the pulse wave measuring processincludes using a computing device to perform the following processactions: a step for employing one or more arterial location sensors toidentify a location on the user's skin in the area proximate to theartery which exhibits the greatest displacement of the user's skin whena pulse pressure wave passes through the artery in the area; a step fordetermining which pressure sensor of the array of pressure sensors isclosest to the identified location on the user's skin; a step forselecting the pressure sensor determined to be closest to the identifiedlocation; and a step for measuring a pulse pressure wave travellingthrough the artery using the selected pressure sensor.

In various implementations, a wearable pulse pressure wave sensingdevice is implemented by means for measuring a pulse pressure wave. Forexample, in one implementation, a wearable pulse pressure wave sensingdevice includes a mounting means which is attachable to a user on anarea proximate to an underlying artery; a pressure sensor array meansdisposed on the mounting means, each pressure sensor of which is capableof being mechanically coupled to the skin of the user proximate to theunderlying artery; and one or more arterial location sensor meansdisposed on the mounting structure which identify a location on theuser's skin likely overlying the artery. The pulse pressure wave ismeasured using the pressure sensor of the array closest to theidentified location.

What is claimed is:
 1. A wearable pulse pressure wave sensing device,comprising: a mounting structure configured to be attachable to a user'sskin on an area proximate to an underlying artery; an array of pressuresensors disposed on said mounting structure, each pressure sensor of thearray being configured to measure a pulse pressure wave travelingthrough the underlying artery; one or more image-based arterial locationsensors disposed on the mounting structure and configured to identify alocation on the user's skin likely overlying the underlying artery, eachof the one or more image-based arterial location sensors beingcalibrated so that pixels in images captured by the image-based arteriallocation sensor are mapped to locations relative to each pressure sensorof the array of pressure sensors; one or more processors; and one ormore storage devices holding instructions executable by the one or moreprocessors to: capture, via the one or more image-based arteriallocation sensors, one or more images of the user's skin, analyze the oneor more captured images to visually identify a location on the user'sskin likely overlying the underlying artery, select a single pressuresensor from the array of pressure sensors that is mapped to theidentified location in the one or more captured images, and measure, viathe single selected pressure sensor, the pulse pressure wave.
 2. Thedevice of claim 1, wherein the pressure sensors in the array of pressuresensors are coated with a skin-sensor interface material having a shapewhich protrudes from the mounting structure so as to contact the skin ofthe user whenever the wearable pulse pressure wave sensing device isworn by the user.
 3. The device of claim 2, wherein one or more of thecoated pressure sensors comprise a single skin interfacing and arterialpressure wave movement transmission layer that is made of a materialthat lays on the skin of the user and transmits arterial pressure wavemovement.
 4. The device of claim 2, wherein the pressure sensors of thearray of pressure sensors are coated with the skin-sensor interfacematerial.
 5. The device of claim 1, wherein the one or more image-basedarterial location sensors identify a location on the user's skin in thearea proximate to the underlying artery which exhibits the greatestdisplacement of the user's skin as said location likely overlying saidartery.
 6. The device of claim 5, wherein the one or more image-basedarterial location sensors comprise reflected optical sensors orultrasonic sensors.
 7. The device of claim 1, further comprising one ormore non-arterial motion sensors disposed on said mounting structurewhich measure the motion of the user's body in the area proximate to theunderlying artery that is not caused by motion of the artery, andwherein a signal or signals output from the one or more non-arterialmotion sensors representing the non-arterial motion of the user's bodyin the area proximate to the underlying artery are employed to remove aportion of a signal output from the pressure sensor of the array ofpressure sensors identified as being most closely overlying the likelylocation of the artery attributable to non-arterial motion.
 8. Thedevice of claim 7, wherein the one or more non-arterial motion sensorscomprise an accelerometer or gyroscope, or both.
 9. The device of claim1, wherein the mounting structure comprises a band which is eitheradhered to the area proximate to the underlying artery, or wrappedaround and tightened against said area.
 10. The device of claim 9,wherein said area proximate to an underlying artery is the user's wrist.11. The device of claim 1, wherein the one or more storage devicesholding instructions executable by the one or more processors to turnoff the pressure sensors of the array other than the selected singlepressure sensor while the single selected pressure sensor is used tomeasure the pulse pressure wave.
 12. The wearable pulse pressure wavesensing device of claim 1, wherein the one or more image-based locationsensors are configured to measure skin displacement of the area on theuser's skin, and wherein the location on the user's skin likelyoverlying the underlying artery is identified based on measurements ofskin displacement of the area of the user's skin via the one or moreimage-based arterial location sensors.
 13. A computer-implementedprocess for measuring a pulse pressure wave travelling through an arteryof a user, comprising the actions of: using a computing device toperform the following process actions: capturing one or more images ofthe user's skin using one or more image-based arterial location sensors,wherein each image-based arterial location sensor is calibrated so thatpixels in the one or more images captured by the one or more image-basedarterial location sensors are mapped to locations relative to each of aplurality of pressure sensors of an array of pressure sensors; analyzingthe one or more captured images to visually identify a location on theskin of the user in an area proximate to the underlying artery whichexhibits the greatest displacement of the user's skin when a pulsepressure wave passes through the underlying artery in said area;determining which single pressure sensor of the array of pressuresensors is mapped to the identified location on the user's skin;selecting the single pressure sensor determined to be mapped to theidentified location; and measuring another pulse pressure wavetravelling through the underlying artery using the selected singlepressure sensor.
 14. The process of claim 13, further comprising turningoff the pressure sensors of the array other than the selected singlepressure sensor while the single selected pressure sensor is used tomeasure the pulse pressure wave.
 15. A system for analyzing a pressurewave travelling through an artery of a user, comprising: a band which iseither adhered to an area proximate to an underlying artery of theuser's body, or wrapped around and tightened against said area; an arrayof pressure sensors disposed on said band, each pressure sensor of thearray being configured to measure a pulse pressure wave travelingthrough the underlying artery; one or more image-based arterial locationsensors disposed on said band and configured to identify a location onthe user's skin likely overlying the underlying artery; an array ofpressure sensors disposed on said band, each of the one or moreimage-based arterial location sensors being calibrated so that pixels inimages captured by the image-based arterial location sensor are mappedto locations relative to each pressure sensor of the array of pressuresensors; and a computing device which executes program modules of acomputer program, the computing device being directed by the programmodules of the computer program to: capture, via the one or moreimage-based arterial location sensors, one or more images of the user'sskin, analyze the one or more captured images to visually identify alocation on the user's skin in the area proximate to the underlyingartery which exhibits the greatest displacement of the user's skin whena pulse pressure wave passes through the underlying artery using thereceived signals output from the one or more arterial location sensors,determine which single pressure sensor of the array of pressure sensorsis mapped to the identified location on the user's skin in the one ormore captured images, select the single pressure sensor determined to bemapped to the identified location, receive a signal output from just theselected single pressure sensor when a pulse pressure wave is travelingthrough the underlying artery, and analyze the received signal tomeasure the pulse pressure wave.
 16. The system of claim 15, wherein theprogram module for analyzing the received signal comprises sub-modulesfor determining at least one of: a heart rate of the user; or variationsin the user's heart rate over time; or the user's augmentation indexwhich is computed using a pulse waveform extracted from said receivedsignal; or a time of arrival of the pulse pressure wave which is used inconjunction with other data to calculate pulse transit time or pulsewave velocity or both.
 17. The system of claim 15, wherein the computingdevice is directed by the program modules of the computer program toturn off the pressure sensors of the array other than the selectedsingle pressure sensor while the single selected pressure sensor is usedto measure the pulse pressure wave.